Antioxidant for rubber



atented Aug. 30, 1932 WILLIAM s. CALCOTT AND W LLIAMA. Because;

:? ramws enovs, New

j SIGNORS won. I. nuroivr m5: nn 'uouns &'coMI'7A1vY, or WiLMINGTON, DELAWARE,

A conroRAT oN or DELAWARE Arr'rIoxImiNr ron RUBBER No Drawing.

This invention relates to a method of V treating rubber for imparting age-resisting qualities thereto and to the resulting rubber products. More particularly, it is concerned 5 with the incorporation, with rubber of certain types of compounds formed by the, reaction of aliphaticaldehydes on aromatic primary amines at low temperatures. 7 a

It is generally accepted that the rate of 1 deterioration of rubber articles differs great- 'ly depending upon various factors among the most important of which is the composition of the stock. Various materials have heretofore been incorporated in rubber stocks to inhibit deterioration, including condensation products of aldehydes with amines.

However, most ofthese agents, and among them the previously employed aldehydeamine condensates have been open to the ob- 2g jection that they cause discoloration of the rubber, especially upon exposure to direct sunlight. i

The primary object of this invention, therefore, is to provide a methodfor retarding the deteriorationof rubber by the use of materials which cause practically no subsequent discoloration even upoii exposure to direct sunlight. V

With this object 'infvievv we have discovered the adaptability for use as antioxidants of a class of compounds not hitherto employed for this purpose. Although the new antioxidants are obtained by the condensation of aliphatic aldehydes witharomatic amines, they are obtained under peculiar conditions and exhibit properties quite different from those products previously employed with rubber and prepared from these compounds at high temperatures.

The method employed in the preparation of these compounds is described in Berichte', Vol. 25, page 2030, and consists in reacting equal molecular proportions of an aliphatic aldehyde, as acetaldehyde, and a primary aromatic amine, as aniline, inthe presence of a solvent as, for example, alcohol, and at temperatures below 10 C. and preferably below 5 C. The antioxidants so prepared cause much less discoloration, on exposure of the vulcanized rubber containing them to light,

Application filed August 13, 1929. Serial No. 385585.

the antioxidants proposedand are particularly valuableyin i m,-

parting to the rubber heat resisting qualities, As an illustration of the preparation of this type o'f compound, the following example is furnished:

Ewample 1 I V V 372g. (4 g. moles) aniline and 372 cc; of alcohol are mixed andflcooled 130,0 O. "A. mixture of 144 g. (100%) acetaldehyde (4 g, moles) and 100 cc. alcohol are gradually added With eflicient-agitation and cooling at such i a rate that the temperature does not riseabove I ,5 0 The timeofthe reactiono depends mainly on the eflic'iency of the. cooling and may require from, 30 minutesto 2,hours. It is advantageous to precool, the 'inixture of. aldehyde and alcohol although this is not necessary. i g p m Agitation is continued maintaining the temperature below 5; G, for at least 1 hour as the additionof the aldehyde is'coinplete. During this time white crystals begin to sep: arate. These crystals, w,hich are the desired product, are filtered off and dried; Themelts r n r ng fm lri p epared in this manner has be en.found ,to;;be 121422? C. V Thisproduct is apparently formed by the reaction: of 2 molecules of amineand 2 molecul'es of 'aldehyde and 'is' believed to beIa stereo isomer. It has been as'signed the fol lovgving formula (Leibigs AnnL'v, 318,?pag 69 AmIZz'doi but l licien'e aniline H on,

* ron it 1'1 liI According to the above "it has the empirical formulaCi I-L N and therefore athe'oretical nitrogenconterit of 11.7%. A eldahhnitrd dic'ated above, are evidently of indefinite constitution. v

In order to make clear the advantages of compounds of-the type described when employed in rubber, the following examples illustrating their 'effectiveness as deterioration inhibitors are presented. It should be understood, however, that theseexamples are furnished purely by .way'of illustration and that it is not the intention that the invention be limited to the particular antioxidant proportions or other conditions therein specified. 7

Example 2 The antioxidant properties of the product obtained by'the method disclosed in Example Tare indicated by the following tests made upon a stock of the composition: 7 P

Smoked sheets. 100 p Zinc oxide 18.15

Sulfur 2.75

Di-o-tolylguanidine 0. 5625 This stock was divided into three parts.

In one part 2.5% of anilido butylidine aniline was incorporated and in another part 5% of thesame compound was incorporated.

The third part was untreated. The three stocks were then cured for 45 minutes at 40 lbs. steam pressure and thecured stocks exposed in an oven at 90 0.. Daily tests of the tensile strength gave the following results: 7

Tensile strength Daysinovenatiw? O. i

Nb antioxidant; 1000 275 3175 3175 1250 2.5'per cent antioxidant 3100 3525 2125 2025 1075 025 3200 3675 2725 2450 2000 1050 5.0 per cent antioxidant v The same stock was aged inthe bomb at C. under 300 lbs. oxygen pressure.v In five days the control was completely deteriorated,- the sample containing 2.5% antioxidant in 20 days, and the sample contain-' ing 5% in 24 days.

Example 3 The discoloring efiect ofsunlight was determined in the following stock: I

r a 7 Parts Pale crepe 100 Zinc oxide 3 Titanox 50' Sulfur ,1 g. .2. Tetramethyl-thiuram-monosulfide 0. 2

Cure 20 minutes at 20 lbs. steam pressure. Samples containing 1% each of the following antioxidants were exposed to direct sunlight under glassfor 7 days. The amount of discoloration was measured by means of-the Lovibond' tintom'eter. The values reported are units of total color on the Lovibond scale. I

. Total Antioxidant color Anili do butylidene aniline; 6.5 Diphenyl ethylene diamine 7. 7 Acetaldehyde aniline acid condensate 13.7 Neozone (phenyl-a-naphthylamine-i-m-toluylene-diarnlne) 31.3

TheTitanox, listed in the aboveformula,

is a mixture of approximately 7 5% barium sulfate and'25% titanium oxide. I

' The above results clearly establish the peculiar value of this compound when employed as an antioxidant in light colored stocks.

In addition to the compcundmentioned above, other products which are obtained by the reaction atlow temperatures of the honio- Am'lz'do octalidene aniline I 5107575515575 baa 7562671.; mam

n13 .tlt

It will be noted thatthe aliphatic aldehydes employed in the preparation of the above compounds all contain at least two carbon atoms since it has-been found that, by reason of the abnormal behaviorof formaldehyde, the products so obtained are not well adapted for use. Of the compounds mentioned, that obtained from aniline and butyproperti'es,frepresents our preferred embodiment. y

According to the formulas which, as noted above, have been already assigned these products in the literature, they have the general formula: I

am at I nHlni-l I I where R and R represent aryl nuclei.

raldehyde, because of its marked preserving Many other compounds of the type listed above could be named. Moreover it is obvious that compounds of the type described may contain non-polar substituents in the aromatic nuclei which substituents would have very little eifect upon the properties of the compounds containing the same.

The new antioxidants may be incorporated into the rubber by any wellknown means, such as by milling them into the stock upon the rolls of an ordinary mill prior to vulcanization. In the above examples they were so incorporated. However, it is often advantageous to treat vulcanized rubber with reagents to improve its aging properties.

This group of antioxidants is particularly useful for this purpose and may be incorporated with the vulcanized rubber by immersing the latter in a solution of the anti-oxidant. Treatment of vulcanized rubber with vapors of compounds of this class will also improve the aging characteristics.

Moreover, the antioxidants may be em treated and, depending upon the protectiondesired and the conditions of exposure to be met, has been found to be highly satisfactory. 7

As many apparent and widely different embodiments of this invention may be made without departing from the spirit thereof, it is to be understood that we do not limit ourselves to the foregoing examples ordescription except as indicated in the following claims.

We claim:

1. The process of increasing the resistance of rubber to deterioration which comprises incorporating with the rubber a compound obtained by reacting substantially equal molecular proportions of butyraldehyde and a primary aromatic amine at temperatures not substantially in excess of 5 C.

V 2. Vulcanized rubber obtained by incorporating with rubber, prior tovulcanizing, a vulcanizing agent and an antioxidant ob tained by reacting substantially equal molecular proportions of butyraldehyde and a primary aromatic amine at temperatures not substantially in excess of 5 C.

3. The process of increasing the resistance of rubber to deterioration, which comprises incorporating with the rubber a compound obtained by reacting substantially equal molecular proportions of butyraldehyde and aniline at temperatures not substantially in excess of 5 C. v 45. Vulcanized rubber obtained by incorporating with rubber prior to vulcanizing a vulcanizing agent and an antioxidant obtained by reactingsubstantially equal molecular proportions of butyraldehyde and aniline at temperatures not substantially in excess of 5 C. r

In testimony whereof we aflix our signa tures.

WILLIAM S. CALCOTT. WILLIAM A DOUGLASS. 

